1. Technical Field
The present invention relates to the oil and gas well drilling, exploration, and production industry. More particularly, the present invention relates to wireline catchers which sense a decrease in wireline tension resulting from a snap, break or any other decrease in tension and responsive thereto catch the line and prevent it from falling into the well bore resulting in a loss of the line and anything attached thereto.
2. General Background
Various devices are known which have been directed to the problem of preventing the falling of a wireline device into a well bore responsive to a break in the line. See, for example, U.S. Pat. No. 3,779,347 entitled "Cable Catcher" issued to Arthur A. Chevalier. In that patent, various other attempts at wireline catchers and/or cable clamping devices and/or grabbing devices are discussed. For example, Marshall provides an early patent (U.S. Pat. No. 1,338,780) which discloses a rope grabbing device to be used as a portable fire escape. Another U.S. Pat. No. (3,179,994) discusses a cable breaking mechanism designed to support a workman physically attached to a vertical cable at an elevated distance.
U.S. Pat. No. 3,467,224 issued to W. L. Curtis, et al, is entitled "Cable Safety Clamping Device for Oil Wells and the Like." In that patent there is provided a housing body having an aperture extending therethrough. The cable to be clamped is normally occupying the aperture. Slips are disposed in a slip way and an actuating device is provided for engaging the slips into the cable when the cable breaks. Fluid pressure is used to move the slips both into and out of engagement with the cable. In order to accomplish the fluid pressure actuation of the slips, upper and lower pistons which are fluid activated bear on the slips themselves.
U.S. Pat. No. 2,991,526 entitled "Scenery Handling Apparatus" was issued to J. F. Kuebler and is a crude example of a type of cable catching device used with rope.
3. General Discussion of the Present Invention
The present invention provides a wireline catching device which comprises a housing having an axial opening through the central portion of the housing which is occupied during operation by a wireline as it descends downwardly toward the well bore. Within the housing body are provided slips which are movable between gripping and retracted positions.
A tripping mechanism in the form of a sheave attached to the wireline is provided, with the slips engaging responsive to breaking of the wireline and a releasing of tension on the sheave. A pair of coil springs normally bias the slips to the retracted position. Pneumatic pressure applied to the slips by means of a ram pushrod actuates the slips.
In the preferred embodiment, releasing of the trip sheave causes a shift in position of an attached pushrod which re-directs and regulates pneumatic pressure from a re-circulating or dormant position to a position which causes the beveled surfaces to engage the slips and press them into position. The invention as disclosed provides an extremely fast reacting and dependable wireline catcher which can catch a broken wireline within a few inches of wireline length after the break occurs.